Various wireless communication systems such as PDC (Personal Digital Cellular), W-CDMA (Wideband Code Division Multiple Access), cdma2000 1x, PHS (Personal Handy-phone System), wireless LAN (Local Area Network) and Bluetooth have conventionally been operated as a mobile communication system. In addition, standardization of high-speed wireless communication such as WiMAX (Worldwide Interoperability for Microwave Access) has been progressed. Each of these wireless communication systems has a different characteristic.
For example, PHS can take many usable terminals per unit area due to small cell area. Therefore it has the advantage of high frequency-use efficiency. In addition, a PHS terminal is required to receive only individual call signals (PCH: Paging Channel) while connecting to a cell station (CS) and its interval is long, thus it has also the advantage of long standby time. However, since the area covered by one cell is small, it has the disadvantage of high possibility of discontinuation of communication when communication is performed while moving at a high speed.
On the other hand, for example, W-CDMA has a wide cell area. Therefore it can be used while moving in a wide range at a high speed. However, a W-CDMA terminal performs despread processing and the like for monitoring incoming calls and a signal level of a cell and the like, therefore its standby time is much shorter than that of the PHS terminal.
Further, with respect to a wireless LAN as typified by widely-used IEEE (Institute for Electrical and Electronics Engineers) 802.11b, hotspots are installed in coffee shops, public facilities and the like and it can communicate at max. 11 Mbps. However, such wireless LAN is provided on the assumption of indoor use, and therefore the cell area is small such as about 10 m in radius.
Moreover, recently, a multimode mobile communication terminal that can use different wireless communication systems seamlessly has been considered. For example, a mobile communication terminal that switches between the wireless communication systems depending on the moving speed of the terminal or depending on a remaining battery level and a determination result of length of standby time in a plurality of wireless communication systems is disclosed in Japanese Patent Application Laid-Open No. 2004-235863.